Abstract

Using leakage-radiation microscopy, we characterize the efficiency of unidirectional surface-plasmon excitation with periodic (800 nm) arrays of 130-nm-high and 330-nm-wide gold ridges on a thin gold film illuminated with a focused (5-μm-wide) laser beam. We demonstrate that, at the resonant wavelength of 816 nm, the excitation efficiency of > 0.4 can be obtained with ≥ 5 ridges by adjusting the beam position. Conducting numerical simulations, we account for the experimental results and calculate the electric-field enhancement achieved near the gold surface.

© 2009 Optical Society of America

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  1. S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
    [CrossRef]
  2. J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
    [CrossRef]
  3. R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
    [CrossRef]
  4. T. W. Ebbesen, C. Genet, and S. I. Bozhevolnyi, "Surface-plasmon circuitry," Phys. Today 61, 44-50 (2008).
    [CrossRef]
  5. H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer-Verlag, Berlin, 1988).
  6. I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
    [CrossRef]
  7. H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
    [CrossRef]
  8. A.-L. Baudrion, F. de Leon-Perez, O. Mahboub, A. Hohenau, H. Ditlbacher, F. J. Garc?a-Vidal, J. Dintinger, T. W. Ebbesen, L. Mart?n-Moreno, and J. R. Krenn, "Coupling efficiency of light to surface plasmon polariton for single subwavelength holes in a gold film," Opt. Express 16, 3420-3429 (2008).
    [CrossRef] [PubMed]
  9. L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
    [CrossRef]
  10. P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972).
    [CrossRef]
  11. E. D. Palik, Handbook of Optical Constants of Solids (Academic, New York, 1985).
  12. I. P. Radko, S. I. Bozhevolnyi, A. B. Evlyukhin, and A. Boltasseva, "Surface plasmon polariton beam focusing with parabolic nanoparticle chains," Opt. Express 15, 6576-6582 (2007).
    [CrossRef] [PubMed]
  13. L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
    [CrossRef] [PubMed]
  14. J.-Y. Laluet, E. Devaux, C. Genet, T. W. Ebbesen, J.-C. Weeber, and A. Dereux, "Optimization of surface plasmons launching from subwavelength hole arrays: modelling and experiments," Opt. Express 15, 3488-3495 (2007).
    [CrossRef] [PubMed]
  15. J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
    [CrossRef]

2008

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

T. W. Ebbesen, C. Genet, and S. I. Bozhevolnyi, "Surface-plasmon circuitry," Phys. Today 61, 44-50 (2008).
[CrossRef]

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

A.-L. Baudrion, F. de Leon-Perez, O. Mahboub, A. Hohenau, H. Ditlbacher, F. J. Garc?a-Vidal, J. Dintinger, T. W. Ebbesen, L. Mart?n-Moreno, and J. R. Krenn, "Coupling efficiency of light to surface plasmon polariton for single subwavelength holes in a gold film," Opt. Express 16, 3420-3429 (2008).
[CrossRef] [PubMed]

2007

I. P. Radko, S. I. Bozhevolnyi, A. B. Evlyukhin, and A. Boltasseva, "Surface plasmon polariton beam focusing with parabolic nanoparticle chains," Opt. Express 15, 6576-6582 (2007).
[CrossRef] [PubMed]

J.-Y. Laluet, E. Devaux, C. Genet, T. W. Ebbesen, J.-C. Weeber, and A. Dereux, "Optimization of surface plasmons launching from subwavelength hole arrays: modelling and experiments," Opt. Express 15, 3488-3495 (2007).
[CrossRef] [PubMed]

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
[CrossRef]

2006

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

2005

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

2003

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

1972

P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

Anker, J. N.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Aussenegg, F. R.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

Bahns, J. T.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

Baudrion, A.-L.

Boltasseva, A.

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

I. P. Radko, S. I. Bozhevolnyi, A. B. Evlyukhin, and A. Boltasseva, "Surface plasmon polariton beam focusing with parabolic nanoparticle chains," Opt. Express 15, 6576-6582 (2007).
[CrossRef] [PubMed]

Bozhevolnyi, S. I.

T. W. Ebbesen, C. Genet, and S. I. Bozhevolnyi, "Surface-plasmon circuitry," Phys. Today 61, 44-50 (2008).
[CrossRef]

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

I. P. Radko, S. I. Bozhevolnyi, A. B. Evlyukhin, and A. Boltasseva, "Surface plasmon polariton beam focusing with parabolic nanoparticle chains," Opt. Express 15, 6576-6582 (2007).
[CrossRef] [PubMed]

Brongersma, M. L.

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

Brown, D. E.

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Brucoli, G.

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

Chandran, A.

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

Chen, L. H.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

Christy, R. W.

P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

de Sanctis, O.

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

Dereux, A.

Devaux, E.

Ditlbacher, H.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

Ebbesen, T. W.

Ebbesen, T.W.

T. W. Ebbesen, C. Genet, and S. I. Bozhevolnyi, "Surface-plasmon circuitry," Phys. Today 61, 44-50 (2008).
[CrossRef]

Evlyukhin, A. B.

Garcia-Vidal, F. J.

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

Genet, C.

Halas, N. J.

S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
[CrossRef]

Hall, W. P.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Hiller, J. M.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Hohenau, A.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

Hua, J.

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Imre, A.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

Johnson, P. B.

P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

Kimball, C. W.

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Krenn, J. R.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

Lal, S.

S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
[CrossRef]

Laluet, J.-Y.

Leitner, A.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

Link, S.

S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
[CrossRef]

Lyandres, O.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Martin-Moreno, L.

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

Pearson, J.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Pellegri, N.

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

Radko, I. P.

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

I. P. Radko, S. I. Bozhevolnyi, A. B. Evlyukhin, and A. Boltasseva, "Surface plasmon polariton beam focusing with parabolic nanoparticle chains," Opt. Express 15, 6576-6582 (2007).
[CrossRef] [PubMed]

Scaffardi, L. B.

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

Schuller, J. A.

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

Shah, N. C.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Tocho, J. O.

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

Van Duyne, R. P.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Vlasko-Vlasov, V. K.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Weeber, J.-C.

Welp, U.

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Yin, L.

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Zhao, J.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Zia, R.

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

Appl. Phys. Lett.

H. Ditlbacher, J. R. Krenn, A. Hohenau, A. Leitner, and F. R. Aussenegg, "Efficiency of local light-plasmon coupling," Appl. Phys. Lett. 83, 3665-3667 (2003).
[CrossRef]

J. T. Bahns, A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, L. H. Chen, and U. Welp, "Enhanced Raman scattering from focused surface plasmons," Appl. Phys. Lett. 91, 081104 (2007).
[CrossRef]

Mater. Today

R. Zia, J. A. Schuller, A. Chandran, and M. L. Brongersma, "Plasmonics: the next chip-scale technology," Mater. Today 9, 20-27 (2006).
[CrossRef]

Nano Lett.

L. Yin, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, J. Hua, U. Welp, D. E. Brown, and C. W. Kimball, "Subwavelength focusing and guiding of surface plasmons," Nano Lett. 5, 1399-1402 (2005).
[CrossRef] [PubMed]

Nanotechnology

L. B. Scaffardi, N. Pellegri, O. de Sanctis, and J. O. Tocho, "Sizing gold nanoparticles by optical extinction spectroscopy," Nanotechnology 16, 158-163 (2005).
[CrossRef]

Nat. Mater.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, "Biosensing with plasmonic nanosensors," Nat. Mater. 7, 442-453 (2008).
[CrossRef]

Nat. Photonics

S. Lal, S. Link, and N. J. Halas, "Nano-optics from sensing to waveguiding," Nat. Photonics 1, 641-648 (2007).
[CrossRef]

Opt. Express

Phys. Rev. B

I. P. Radko, S. I. Bozhevolnyi, G. Brucoli, L. Mart?n-Moreno, F. J. Garc?a-Vidal, and A. Boltasseva, "Efficiency of local surface plasmon polariton excitation on ridges," Phys. Rev. B 78, 115115 (2008).
[CrossRef]

P. B. Johnson and R. W. Christy, "Optical constants of the noble metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

Phys. Today

T. W. Ebbesen, C. Genet, and S. I. Bozhevolnyi, "Surface-plasmon circuitry," Phys. Today 61, 44-50 (2008).
[CrossRef]

Other

H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings (Springer-Verlag, Berlin, 1988).

E. D. Palik, Handbook of Optical Constants of Solids (Academic, New York, 1985).

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Figures (4)

Fig. 1.
Fig. 1.

(a) SEM image of a fragment of the fabricated structure consisting of 130-nm-high and 330-nm-wide ridges. (b) Geometry of the illumination configuration. (c) Typical LRM image of a strong SPP beam excited on the 11-ridge array on its left side. A much weaker SPP beam propagating to the right is also visible.

Fig. 2.
Fig. 2.

(a) The maximum efficiency of SPP excitation obtained experimentally for different laser wavelengths as a function of number of ridges. The lines connecting the points are only to guide an eye. (b) Experimental and numerical results for the SPP excitation efficiency versus the position of a laser beam scanned across the 11-ridge array extending from x = 4 μm to x = 12 μm. Error bars both in (a) and (b) are omitted for clarity of presentation. The error of measurements is estimated to be ~ 13%.

Fig. 3.
Fig. 3.

Numerical results for electric-field amplitude distribution near the 11-ridge array illuminated under the optimal conditions for SPP excitation. The field values are normalized to the amplitude of the incident field.

Fig. 4.
Fig. 4.

(a) SEM image of a circularly curved 11-ridge array. (b-d) LRM images of SPP excitation and focusing at the laser wavelength of 816 nm. An approximate position of the arrays is shown with the dashed curves. Internal radii of curvature of the arrays are (b) 28.8 μm, (c) 9.6 μm, and (d) 4.8 μm.

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